(a) Technical Field
The present invention relates to a metallic porous body for a fuel cell. More particularly, the present invention relates to a metallic porous body for a fuel cell, which has improved handling and working properties and can be accurately and precisely stacked, thereby improving the productivity of a fuel cell stack as well.
(b) Background Art
A fuel cell is an electrical generation system that does not convert the chemical energy of fuel into heat by combustion, but rather electrochemically converts the chemical energy directly into electrical energy in a fuel cell stack. Fuel cells can be used as an electric power supply for small-sized electrical and electronic devices, including, for example, portable devices, industrial uses, household appliances and vehicles.
One of the most widely used fuel cells for vehicles, in particular, is a proton exchange membrane fuel cell or a polymer electrolyte membrane fuel cell (PEMFC), which made up of a fuel cell stack having a membrane electrode assembly (MEA), a gas diffusion layer (GDL), a gasket, a sealing member, and a bipolar plate (separator). Generally, the MEA includes a polymer electrolyte membrane, through which hydrogen ions are transported and an electrode/catalyst layer, in which an electrochemical reaction takes place, is disposed on each of both sides of the polymer electrolyte membrane. The GDL functions to uniformly diffuse reactant gases and transmit generated electricity. The gasket functions to provide the appropriate air-tightness to reactant gases and coolant. The sealing member functions to provide an appropriate bonding pressure. Finally, the bipolar plate functions to support the MEA and GDL, collect and transmit generated electricity, transmit reactant gases, transmit and remove reaction products, and transmit coolant to remove reaction heat, etc.
The GDL is bonded to the outer surface of the electrode/catalyst layer, which is coated on the surface of the polymer electrolyte membrane to form an anode (“fuel electrode) and a cathode (“air electrode” or “oxygen electrode”) and functions to supply hydrogen and air (oxygen) as reactant gases, transfer electrons generated by the electrochemical reaction, and discharge reaction product water to minimize flooding in the fuel cell.
Recently, there has been extensive research around the world focused on the application of a thin metal plate having a mesh structure instead of carbon fiber, to the GDL of the fuel cell, i.e., a porous structure such as an expanded metal, a metal mesh, etc.
FIG. 1 shows metallic porous bodies which can be used as the GDL of the fuel cell, in which (a) shows an example of an expanded metal porous body and (b) shows an example of a metal mesh porous body. The expanded metal 1 shown in (a) of FIG. 1 is an example of a porous plate having a plurality of rectangular apertures formed by pressing or rolling a metal plate, and the metal mesh 2 shown in (b) of FIG. 1 is an example of a porous plate formed by weaving a plurality of wires 2a in a mesh shape.
These metallic porous bodies having regular porous structures can exhibit uniform performance during use in the fuel cell and reduce the deviation between the cells. Moreover, the diffusion of reactant gases is improved and the discharge of water is efficient, thus contributing to the improvement of fuel cells overall performance.
However, even in the case where these metallic porous bodies 1 and 2 are used as the GDLs, each of the metallic porous bodies 1 and 2 are stacked together with fuel cell components such as the MEA, separator, gasket, etc. in the same manner as conventional methods, thus completing the fuel cell stack.
Conventionally, the metallic porous bodies 1 and 2 shown in FIG. 1 are cut into a size suitable for a reactive area on the separator of the fuel cell (i.e., a reactive area of the membrane electrode assembly), simply placed on the separator, and then assembled with the separator. Here, each of the metallic porous bodies 1 and 2 are a separate component, which are not integrated with any other fuel cell components.
These metallic porous bodies have sharp outer edges formed during cutting due to the nature of the material and, when the conventional metallic porous bodies are used without any modification, the handling and working properties are deteriorated due to the sharp outer edges formed during cell assembly.
In particular, the sharp outer edges of the metallic porous bodies are more likely to damage pin apertures of the membrane electrode assembly, which are in contact with the sharp outer edges during cell assembly, thus deteriorating the overall performance of the fuel cell stack.
Moreover, since the conventional metallic porous bodies are separate components, which are not integrated with any other fuel cell components, the arrangement of the metallic porous bodies becomes irregular during cell assembly, and thus the metallic porous bodies cannot be accurately and precisely stacked. Further, an automatic assembly (stacking) method such as air suction cannot be employed, which reduces the productivity of the fuel cell stack. In an automatic assembly (stacking) method such as air suction, metallic porous bodies must be transported in a state where they are adsorbed on the suction device. However, due to the presence of many pores on the surface (i.e., lack of flat surface) of the metallic porous bodies, it is difficult to have a stable adsorption between the metallic porous bodies and the suction device. Therefore, to obtain a stable adsorption it is essential that the suction device adsorb to a non-porous flat surface.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.